In an engine starting device of the related art, in order to mitigate the shock at the time of collision of each edge surface of the pinion and the ring gear when the pinion is engaged with an engine starting gear such as a ring gear (hereinafter, referred to as a “ring gear”), there has been known a structure in which a pinion can be moved by a spring or the like so as to decrease a force for pushing a ring gear with an inertia force at the time of engaging the pinion. Since only the pinion can be moved, an impact force at the time of collision is converted into mass of only the pinion, it is possible to decrease a collision energy, noise is reduced and the durability is improved (for example, Patent Citation 1 and 2)
[Patent Citation 1] JP-A-2006-161590 (Abstract, FIG. 2 and the description thereof)
[Patent Citation 2] JP-A-2009-138656 (Abstract, FIG. 2 and the description thereof)